The present invention generally relates to an electrical part and more particularly, to a capacitance and resistance composite part or CR composite part (referred to as CR composite part hereinbelow) provided with a gap for electrical discharge.
In a conventional CR composite part of the above described type, it is so arranged, for example as shown in FIG. 1, that two electrode layers 2-1 and 2-2 are provided on one surface 1a of a substrate 1 made of a dielectric material, while a common electrode layer 3 is formed on the other surface 1b of said substrate 1 so as to form capacitors C1 and C2 between the electrode layers 2-1 and 3, and the electrode layers 3 and 2-2, with the respective electrode layers 2-1 and 2-2 being further formed with discharge electrode layers 4-1 and 4-2 confronting each other at corresponding forward ends thereof through a predetermined interval. The electrode layers 2-1 and 2-2 are further bridged by a resistant layer 5, and respectively connected to lead wires l1 and l2.
The CR composite part as referred to above may be represented by an equivalent circuit shown in FIG. 2.
In the known CR composite part as described above, however, since both of the discharge electrode layers 4-1 and 4-2 are provided on the same surface 1a of the substrate 1 for electrical discharge therebetween on said surface 1a, there have been such disadvantages that, if foreign matters such as dust and dirts, vapor, etc. in the atmosphere should adhere to the surface of the substrate 1 between the discharge electrodes 4-1 and 4-2, discharge starting voltage between said discharge electrodes 4-1 and 4-2 is unnecessarily lowered, with undesirable heating of such foreign matters during the electrical discharge. Moreover, owing to the fact that both of the discharge electrode layers 4-1 and 4-2 are disposed comparatively close to each other in the prior art arrangement as described above, a stray capacitance is formed therebetween, thus also resulting in an undesirable lowering of the discharge starting voltage. Accordingly, there have been required countermeasures such as enlargement of the gap between the discharge electrodes 4-1 and 4-2 or application thereto of a voltage withstanding reinforcing agent, thus making it difficult to reduce the size of the CR composite part by that extent, with consequent troublesome procedures and high cost required for manufacture thereof.